Title：Seed dormancy and germination of the medicinal holoparasitic plant Cistanche deserticola from the cold desert of northwest China
Cistanche deserticola is a holoparasitic plant with high medicinal value that reproduces only by seeds. However, the requirements for seed dormancy break and germination of this species remain unclear. The freshly matured dust-like seeds consist of a water-permeable seed coat and an undifferentiated oval-shaped embryo embedded in endosperm. No fresh seeds germinated in water or a 10-5 Mfluridone solution at any incubation temperature within 60 days. Length of embryos in seeds incubated in warm- and cold-started stratification sequences had increased 10.4 and 11.7 % after 50 and 40 weeks, respectively. After 6 months, length of embryos in seeds stratified at 5 ºC had increased by 12 %. Germination of fresh seeds and of seeds stratified at 5 ºC for 6 months and then incubated in mixed fluridone/gibberellic acid 3 (GA3) solutions at 30/20 ºC germinated to only 2.6 and 11.7 %, respectively. Embryos of fresh seeds and of cold-stratified seeds had increased 29.4 and 15.8 % in length, respectively, at the time of germination, but they never differentiated into organs. The highest germination (54.4 %) was for seeds incubated in a 10-5 Msolution of fluridone in darkness in spring that had overwinter on the soil surface in the natural habitat. Our study indicates that breaking of physiological dormancy (PD) occurs first and then the embryo grows to a critical length (0.44 mm) without differentiation into organs prior to seed germination. Seeds for which PD had been broken were induced to germinate by fluridone and GA3 at high temperature. Taken together, these results suggest that C. deserticola seeds have a specialized kind of morphophysiological dormancy. This study reveals possible ways to release seed dormancy that will be useful in propagating this medicinal species.